Home and dry: Sustainable station heating

Monday 8 December 2014

In case you hadn’t noticed, Winter is upon us again. Nights are drawing in, the central heating has choked back into life, and we’re all wrapping up and battening down.

Our volunteer crews carry on regardless, whatever weather the season throws at them. You only have to check our news page to see that most days bring another lifeboat rescue in pretty difficult conditions. Right now, an RNLI crew near you is on call – willing to drop everything to save lives.

We often talk about how your donations provide these volunteers with the cutting-edge lifeboats and protective kit they need when out at sea. But what about when they return from the storm on a freezing Winter night, wet and exhausted? What would you look forward to?

I love a nice hot cup of tea! But I appreciate it all the more when I've changed into my toasty warm, dry clothes and it's there, ready and waiting, already made by one of our lovely crew who stayed ashore.

Lucy Heathfield, Burnham-on-Crouch lifeboat crew member

Photo: RNLI/Adrian Don

Redcar crew relax with a brew after rescuing a father and son who were thrown from their fishing boat in July 2014

The heat is on

Getting warm and dry would probably be near the top of your list. Sounds pretty basic but providing that, on-demand, at more than 235 lifeboat stations presents a unique set of challenges. No two lifeboat stations are the same and many are in hostile locations. So how does the RNLI maintain so many welcoming environments in a reliable, cost-effective and green manner?

‘Traditionally, our crews relied on just electric heaters,’ admits RNLI Estates Engineer Rob Jeans. ‘Of course, you never know when you need to use a station and, if you’re arriving at 2am on a February morning, you need instant heat. That’s where convection heaters are handy. But they don’t give out a particularly good heat.’

Crews need to dry their kit after a shout too – and keep it that way to stop it deteriorating. Electric drying tubes and dehumidifiers do that job but they need to be running all the time. Too much dry heat makes for quite an oppressive changing room and it damages kit. ‘I remember at one station, the dehumidifier had even dried out the traps in the toilet!’ says Rob. ‘The trouble is, if you shut it all down the kit quickly gets damp again.’

And all that adds up on our electricity bill. Regulation is ever tighter too – getting permission to install this heating can bring challenges. So, in 2006, Rob and his colleagues set to work on a solution. Several thermodynamic calculations and modellings later, they realised the answer was right under their feet – quite literally. They could use heat pump technology, taking naturally occurring heat from the ground.

What on earth?

A ground source heat pump is a system that extracts low-grade heat from the earth, amplifies it using the natural laws of physics and a little electricity (see How does it work? below), and circulates it beneath the station floor. So you’re not getting something for nothing but, for every 1KW you use powering the heat pump, you get 4KW of useable heat out. ‘There’s nothing revolutionary about heat pump technology,’ says Rob. ‘But including it as part of a new lifeboat station build was fresh thinking.’

In 2007 the team installed a ground source system at Exmouth Lifeboat Station. ‘It’s very efficient,’ says Rob. ‘It holds the station at 16°C. That’s ideal workshop temperature and comfortable all day for the mechanic doing his work. It keeps crew kit in it better condition and, if you are there on that chilly February morning, it’s plenty warm enough to get changed and launch the lifeboat.’

Of course, there’s still a need to do things quickly – that’s the very nature of the RNLI’s work. Drying tubes still flush the kit dry after a shout but they no longer need to stay on. The new system effectively turns the changing room into an airing cupboard. ‘The lads at Exmouth will tell you that they barely use the drying tubes now because their kit is kept dry and well-aired,’ says Rob.

The under-floor heating proved to be one of the best assets of our new station. In the Winter I often arrived at the station on my motorbike cold and wet. I used to leave my kit on the floor, while in a hurry to get the boat launched, and it was all dry on my return!

Tim Mock, Former Exmouth Coxswain

Admittedly, you’ll still find an electric heater in the crew room but a quick blast is now all that’s needed to top up the heat for a crew meeting on a chilly night.

‘Overall it’s a much better environment for crew and survivors,’ says Rob. ‘It keeps the fabric of the building in good order, it’s better for the planet – and it slashes RNLI energy bills. There are so many benefits.’

Salt water, fresh thinking

Following this success, Rob’s team have been installing similar systems in every new RNLI lifeboat building. Today, there are 10 ground source installations up and running, and many more in the pipeline.

But they hit a stumbling block when planning the new boathouse build at The Lizard – this unique slipway station is a long way from the ground and surrounded by rock. ‘It would have cost us a fortune to run pipework up the cliffs to collect ground heat,’ explains Rob. ‘That set us thinking about using seawater as a source of heat instead. After some careful calculations we knew we could make it work.’

But the proposal was met with much sucking of teeth by industry experts. Nothing was commercially available and everyone, from consultants to suppliers, warned of saltwater corrosion. This is a familiar enemy of the RNLI, as an organisation we have been tackling seawater for 190 years. Rob and the team just needed a way of extracting the heat and passing it through the system separately.

‘We approached industrial process companies – people that are used to dealing with corrosive materials and transferring heat. With their help, we built our own trial unit at RNLI Headquarters in 2010,’ he says. ‘We kept a 1-tonne tank of water at 35°C throughout the Winter – just by taking seawater out of Poole Harbour! It was a brilliant demonstration of how it could work. And from that we refined the filtering system.’

The team installed their first water source heating system as part of the new build at The Lizard in 2011. ‘We’ve installed four more since then and more are in planning,’ says Rob. ‘Now, we have choices. We look at what environment we’re dealing with and select the most effective heat source for that particular lifeboat station.’

How does it work?

First, you need some naturally occurring heat. The RNLI’s water source system collects this from seawater at the lifeboat station. It’s extracted at around 7°C through a series of filters off the seabed.

The filtered water then enters a platepack heat exchanger. This comprises a series of thin titanium plates that hold seawater one side and a biodegradable heat-transfer fluid (which is colder than the seawater) on the other. The two liquids are separate but the natural laws of physics means that the energy transfers from the warm space (seawater) to the colder space (the heat-transfer fluid). There are 50 plates in total, creating a massive surface area. Around 5°C is transferred.

In the case of a ground source system, the heat-transfer fluid is circulated in the ground through a loop system, known affectionately as a slinky. These slinkies often lie horizontally but, if you’re tight on space, boreholes can be created to seat them vertically. The ground's temperature averages at 10°C, and doesn't vary much from Summer to Winter. The heat-transfer fluid absorbs the heat using the same physics as above.

The warm heat-transfer fluid then enters the heat pump, which condenses and amplifies the heat to around 35°C. The process is a bit like that of a fridge in reverse. Imagine chilling a bottle of Prosecco at home. Your fridge creates a cycle of compression and evaporation which removes the wine’s heat and pumps it through the coiled set of pipes at the back. The heat radiates out continually, eventually turning the wallpaper behind it brown and attracting spiders. Now try to imagine the sea is that bottle of Prosecco … you’re cooling it but, rather than treating the displaced heat as an annoying by-product, it’s put to good use in underfloor heating. The newly-chilled seawater is the by-product that is pumped out to sea to warm again naturally. There may still be spiders.

Illustration: RNLI/Chris Speers

How the water-source heat pump at The Lizard Lifeboat Station keeps this extreme crew warm

Underfloor heating may sound extravagant, but it’s quite the opposite. Its heating loops only need water at 35°C to create a comfortable environment. A boiler and radiator system needs water double that temperature to create the same effect.

Sharing innovation

Energy prices are going up, so the RNLI is not alone in thinking about this technology. ‘I think we’re definitely at the start of the curve though,’ says Rob. ‘The Department of Energy and Climate Change asked us to speak at one of their seminars.’

Rob and the team have also been sharing their knowledge with the National Trust. ‘They were very interested in our water source heat pumps,’ he says. We shared our experiences, which assisted with a new heating system for a country home on Anglesey. The trust had its own ideas too, of course. It’s a bigger system, using slightly different materials, so we may learn something useful in return that will help us carry on refining our own systems.

What about sun and wind?

It’s not all about heat pumps. The RNLI also has 20 solar installations – and a wind turbine. ‘This year we’ve generated 550MWhrs in renewable energy,’ says Rob. ‘That’s 5% of the RNLI’s total electricity use. Heating at Exmouth Lifeboat Station is carbon neutral. Its solar panels produce more energy than is needed to drive the ground source heat pump. We sell that back to the grid.’

This eco-friendly technology needs investment upfront but the payback will be considerably more over the life of the installations. ‘For every £1 of supporters’ money we invest in renewables, that’s £2-£3 back for front-line services,’ Rob says. ‘And we’re cutting our carbon footprint at the same time.’